It is known, in cyclone type melting furnaces, how to cause finely divided vitrifiable raw materials to flow onto the strongly inclined or vertical walls of revolution. In such construction, the material is heated by jets of hot gases introduced tangentially to the walls. The raw material must be finely divided so that under the dynamic action of the gas jets, it is distributed homogeneously and flows with a slow enough speed to be able to melt during its travel. The drawback of these devices is a segregation of the raw materials deposited on the wall causing heterogeneities during melting.
In copending U.S. application Ser. No 602,670 filed Aug. 7, 1975, now abandoned, entitled "Method and Apparatus for the Manufacture of Glass", a rapid glass refining process is described in which a raw vitreous mass is brought to an elevated temperature while maintaining the viscosity of the molten mass at less than 1000 poises. Then, an intense foaming of this molten mass is effected throughout its entire thickness while keeping the viscosity at a value less than 1000 poises. The rate of expansion of the mass is at least about 1.5. After the end of the foaming, a perfectly refined glass is collected. The present invention relates to a prefusion process and devices that can advantageously be used in association with the process described in said copending application.